Non-linear optical crystals, such as lithium niobate and lithium tantalate single crystals, have high secondary non-linear optical constants. A periodic polarization inversion configuration can be formed in the crystal to produce a Quasi-Phase-Matched (QPM) Secondary-Harmonic-Generation (SHG) device. Further, an optical waveguide may be formed in the periodic polarization inversion configuration to produce a high efficient SHG device, leading to a wide variety of applications in optical communication, medical, photochemical and various optical measurement fields.
According to Japanese patent publication No. 2005-55528A filed by the assignee, a semiconductor laser oscillating device of Fabri-Perro type is used to oscillate light, which is then irradiated into a slab-type optical waveguide made of a non-linear optical crystal as fundamental wave to output blue-ray laser from the slab optical waveguide. The slab-type optical waveguide is produced by polishing a Z-plate of the non-linear optical crystal such as lithium potassium niobate.